1. Field of the Invention
The present invention generally relates to a connection establishing system in ATM (Asynchronous Transfer Mode) which is a communication mode Suitable for a B-ISDN (Broadband-Integrated Services Digital Network). More particularly, the present invention relates to a system for establishing connection to transfer a remote maintenance ATM cell, transmitted from a remote maintenance terminal, to a remote maintenance control section.
2. Description of the Related Art
Due to the recent popularity of data communications, multimedia communications for transmitting data, such as voices, images and codes, are executed using a public network. Accordingly, the practical use of a broad-band ISDN which can permit fast data communications of 150 to 600 Mbps has begun. In this broad-band ISDN, an ATM system is employed as a basic transfer exchange system. In the ATM system, every piece of communication data of different bands is separated into cells of a fixed length (53 octets). A plurality of cells belonging to different calls are transferred in a mixed fashion in a transmission path. Those cells are switched properly by hardware.
In such an ATM system, PVC (Permanent Virtual Connection) can be established. The PVC is to set a specific virtual channel (VC) in a semi-fixed manner between specific subscriber terminals. Such PVC is therefore suitable for use in communications between branches of the same corporation, for example.
PVC is made by causing a maintenance terminal connected to one node to send a remote maintenance ATM cell to the remote maintenance control section at each node. Before establishing PVC, therefore, it is necessary to establish an ATM remote maintenance connection to transfer this remote maintenance ATM cell to the remote maintenance control section of each node from the maintenance terminal.
In some cases, a remote maintenance ATM cell may have to be sent to the node to which PVC should be established, from the maintenance terminals connected to the other nodes. One example of such cases is to establish PVC to a plurality of nodes (exchanges). In such a case, it becomes necessary to establish PVC to the individual nodes which are concerned with the PVC. When remote maintenance or file transfer is executed to those nodes after establishing the PVC, it becomes necessary to transfer a remote maintenance ATM cell for remote maintenance and file transfer.
According to a conventional ATM remote maintenance connection establishing system, however, a remote maintenance ATM cell could not be transferred fixed remote maintenance connection was established in advance. In other words, a remote maintenance ATM cell could not be sent from the maintenance terminal to which no fixed remote connection was established. For the same reason, a remote maintenance ATM cell could not be sent via a trunk to the node which is demanded the establishment of PVC, from the maintenance terminals connected to the other nodes.
In establishing PVC to a plurality of nodes, therefore, fixed remote maintenance connection should previously be made from local maintenance terminals connected to the individual nodes which is requested the establishment of PVC, and an ATM cell for ATM remote maintenance should be transmitted to establish the PVC. This case inevitably raises the following shortcomings. If PVC has been established erroneously at the time of channel initialization, it is difficult to localize which node has the wrong establishment. If a remote maintenance connection needs to be changed after channel operation due to some channel problem, channel expansion, etc., a maintenance personnel or operator should personally go to the site of such a node.